It is commonly known that the structure of absorbent products which are used in order to absorb and retain liquids that are produced from the body involves an absorber, which absorbs and retains liquids, interposed between a surface material, which is permeable to liquids, and a leak-proof material, which is impermeable to liquids. In such absorbent products, aside from the obvious characteristic of quickly transferring the liquid to be absorbed to the absorber, it is necessary that the liquid-permeable surface material (which is also sometimes referred to as the outer wrapping, covering, top sheet or cover stock) does not give an unpleasant feeling to the user by not allowing backflow of the liquid that has moved into the absorber (to be referred to as backflow prevention), does not give an unpleasant feeling to the user by not allowing the surface to become stained when absorbing colored liquids such as fecal material or blood (to be referred to as stain prevention), does not allow the liquid that has been absorbed into the absorber to leak from the ends of the sanitary article through the surface material, and also provide adequate ventilation.
In order to achieve this objective, various proposals have been made and techniques to improve upon these proposals are also numerous.
Specifically, to begin with, instead of hydrophilic materials such as pulp or rayon which have been typically used in the past for the component materials of the surface material, there is an example of the prior art which improves the prevention of backflow by the formation of a region of hydrophobic atmosphere between the surface of the body and the absorber using hydrophobic synthetic fibers such as polyolefine and polyester (Pat. Disclosure SHO 58-180602). Although backflow prevention is improved considerably as a result of this, there is an inevitable occurrence of a reduction in liquid permeability.
Therefore, although techniques have been proposed which allow both liquid permeability and backflow prevention to co-exist by composing the surface material blending both hydrophobic fibers and hydrophilic fibers (Pat. Disclosure SHO 55-68367, Pat. Disclosure SHO 57-136454) or using a hydrophobic fiber following hydrophilic treatment of the surface (Pat. Disclosure SHO 54-163136), in these methods, it still remains extremely difficult to make these two properties compatible with each other.
In addition, other techniques have been proposed which attempt to solve the above problems by providing holes in hydrophobic nonwoven fabric or film and placing a hydrophilic fiber beneath it, followed by further allowing the lower hydrophilic fiber to penetrate to the surface of the holed portion (Pat. Disclosure SHO 57-1339, Utility Model SHO 62-20194, and Pat. Journal SHO 59-36534).
However, in the case of actually using such surface materials, when pressure is applied due to movement of the user, since liquid that has migrated to the absorber easily transfers to the body surface, backflow prevention was inadequate. Moreover, since the lower hydrophilic fiber layer is visible through the holes, stain prevention was poor.
On the other hand, although there were also techniques which solved the above problems by extending hydrophilic fibers into a hydrophobic surface material using fluid differential pressure or needle punch, etc. (Pat. Journal SHO 59-32456), since effectively extending the hydrophilic fibers is extremely difficult in consideration of the accompanying complexity of the manufacturing process, the anticipated effectiveness was not obtained.
In this manner, the prior art was unable to obtain a surface material having both superior liquid permeability and backflow prevention, and this became a major obstacle in improving the performance of absorbent products resulting in a solution being hoped for as soon as possible.